Dam Decommissioning

by Patrick McCully, Executive Director, International Rivers

Dams do not live forever. A dead or dying dam may have silted up, stopped producing electricity, or become increasingly unsafe, at which point it may be a candidate for removal. Not all dams slated for removal are targeted for safety reasons, however: another major reason prompting activists to call for the removal of dams is the decimation of fisheries.

Although dams have been found unsafe or destructive of fish habitat in many parts of the world, few major dams have yet to be removed. The engineering of dam removal is still young and untried, and the cost of dam-removal is still ignored when construction costs are estimated. How exactly to dismantle a very large dam, what to do with the sediment clogging the reservoir behind it, and how much such an operation would cost, is largely unknown. Removing a hydrodam could even cost more than building one, especially where reservoir sediments contain heavy metals and other toxic contaminants.

But momentum is building to remove more dams, and to find the best ways to take them down and restore the rivers they impounded. Dam removal campaigns are now underway in many parts of the world, some of which target very large dams. Currently, the United States - with some 74,000 dams (most of which are relatively small) - has perhaps the most active dam-removal movement. Grassroots groups around the country have launched campaigns to dismantle dams in their communities, and hundreds of small- and medium-sized dams have already come down. Another sign of progress is that the American Society of Civil Engineers just published technical guidelines for dam removal - the first important sign that the dam-building industry is beginning to take this issue seriously.

Old DamsSafety concerns have been the most common reason for dam removals. Dams age at a different rates and in a different way, depending on a variety of circumstances. Some dams may remain safe for a thousand years, others may start to crack and leak after less than a decade. Around the world, some 5,000 large dams are now more than 50 years old, and the number and size of the dams reaching their half century is rapidly increasing. The average age of dams in the US is now around 40 years. Between 1977 and 1982 the Army Corps of Engineers inspected 8,800 non-federal dams in the US, most of them privately-owned, which it classified as "high-hazard" - where a failure could cause significant loss of life. One-third of these dams were considered "unsafe," primarily because of inadequate spillway capacity. A 1994 survey showed at least 1,800 non-federal dams were still unsafe. The situation is similar for federal dams: in 1987 one-fifth of BuRec’s 275 dams were classified as unsafe, as were one-third of the 554 dams operated by the Corps of Engineers.

An Ontario Hydro study of data from several hundred North American dams shows that on average hydrodam operating costs rise dramatically after around 25-35 years of operation due to the increasing need for repairs. When the cost of maintaining an old dam exceeds the receipts from power sales, its owners must decide either to invest in rehabilitating the dam, or, if the cost of repairs would be prohibitive, to disconnect the dam from the grid and cease producing power.

Many old dams in the US have simply been abandoned by their owners. According to the Michigan Department of Natural Resources (MDNR), several abandoned small dams have been washed out during storms in recent years. "These failures," says the MDNR, "have caused extreme erosion, excessive sediment deposition and destruction of aquatic habitat accompanied by the loss of the fisheries." Michigan taxpayers, through the MDNR, have had to pay for removing several "retired" hydroelectric projects, while their ex-owners have suffered no financial liabilities.

Restoring the ElwhaThe best-known dam decommissioning controversy surrounds a pair of dams that decimated fisheries on the Elwha River in Washington State: the 31-meter Elwha and 70-meter Glines Canyon Dams. Built in the 1910s and 1920s with a combined installed capacity of 19 megawatts, the dams all but wiped out the river’s once-rich runs of steelhead trout and salmon, fisheries to which the Elwha S’Klallam Tribe had been guaranteed rights "in perpetuity" in the remarkably aptly named 1855 Treaty of Point No Point. Power from the two dams (now within the borders of Olympic National Park) is devoted entirely to supplying a pulp and paper mill. Since the Glines Canyon Dam FERC license came up for renewal in the late 1970s, the Lower Elwha S’Klallam and environmentalists have been trying to get the dams removed. In 1992 their long campaign started to bear fruit when Congress directed the Interior Department to detail the best plan for "full restoration of the Elwha River ecosystem and the native anadromous fisheries." The Interior Department concluded that only removing the dams could fully restore the ecosystem.

Visit International Rivers’s River Revival project web page to learn more about subsequent developments in the dam decommissioning movement!